TEE PORTAL CIRCULATION. 



209 



vein, which enters the liver, and breaking up there into 

 finer and finer branches like an artery, ends in the 

 capillaries of that organ, forming 

 the second set which this blood 

 passes through on its course. 

 From these it is collected by the 

 hepatic veins, which pour it into 

 the inferior vena cava which car- 

 ries it to the right auricle, so that 

 it has still to pass through the 

 pulmonary capillaries to get back 

 to the left side of the heart. The 

 portal vein is the only one in the 

 human body which thus like an 

 artery feeds a capillary network, 

 and the flow from the stomach 

 and intestines through the liver 

 to the inferior vena cava, is often 

 spoken of as i\iQ portal circulation. 

 Diagram of the Circulation. 

 Since the two halves of the heart, 

 although placed in proximity in 



FIG. 63 Diagram of the 

 blood vascular system, show- 

 ing that it forms a single 

 closed circuit with two pumps 

 in it, represented by the right 

 and left halves of the heart, 

 which are separated in the 

 diagram, ra and rv, right aur^- 

 cle and ventricle; la and Zv, 



., . , ,, , . , left auricle and ventricle; ao, 



the body, are actually Completely aorta; sc, systemic capilla- 

 ries; vc, venae cavre; pa, pul- 



Separated from One another by an monary artery ;pc,pulmonary 



capillaries; pv, pulmonary 



impervious partition, we may con- veins. 

 veniently represent the course of the blood as in the ac- 

 companying diagram (Fig. 63), in which the right and 



Where does this vein carry it? In what does it end? Into 

 what vessels is the blood of the capillaries of the liver collected? 

 Where do they convey it? What chamber of the heart does it 

 first reach? Through what must it pass to get back to the left 

 ventricle? How does the portal vein differ from all others in the 

 body? What is meant by the portal circulation? 



